98 THE BONES. 



SHOULDER. 



In Solipeds, this region has for its base a single bone — the scapula or omoplat. 

 ^^ Scapula (Figs. 59, 60). 



This islW»^ triangular, and asymmetrical bone, prolonged at its superior 

 border by a flexible cartilage, articulated interiorly with the humerus only, and 

 applied against the lateral plane of the thorax in an oblique direction downwards 

 and forwards. It has two faces, three borders, and three angles. 



Faces. — The external face (or dorsum) is divided by the scapidar or acroynian 

 spine, into two cavities of unequal width — the supra- and infra-spinous (or antea 

 and 2)ostea spinatus) fosscB. The spine is a very salient crest which runs the whole 

 length of the external scapular surface ; very elevated in its middle part, which 

 shows an irregular enlargement — the tuberosity of the spine — it insensibly decreases 

 towards its two extremities. The supraspinous fossa — the narrowest — is situated 

 above, or rather in front of the spine ; it is regularly concave from side to side, 

 and perfectly smooth. The infra-spinous fossa is twice the width of the preceding, 

 and occupies all the surface behind the spine. It exhibits : 1. Below, and near 

 the posterior border, several rows of roughened lines for muscular insertion. 

 2. Near the neck, the nutritient foramen of the bone, and some vascular grooves. 



The interned face is excavated in its centre to form a hollow, called the subsca- 

 pular fossa, which is prolonged superiorly by three diverging points. The median 

 point extends to the superior border of the bone, and separates two roughened 

 triangular surfaces. 



Borders. — The superior is indented by an irregular groove, to receive the 

 inferior margin of the cartilage of prolongation. The latter is convex on its 

 superior border, extends beyond the posterior angle of the bone, and gradually 

 diminishes in thickness as it leaves its point of attachment. In old horses it is 

 nearly always found partially ossified. The anterior border, thin and sharp, is 

 convex in its superior two-thirds, and slightly concave for the remainder of its 

 extent. The posterior is thicker and a little concave. 



Angles. — The anterior, or cerviccd angle, is the thinnest of the three. The 

 posterior or dorsal angle is thick and tuberous. The inferior, or humeral angle, is 

 the most voluminous, and is separated from the remainder of the bone by a 

 slight constriction, which constitutes the neck of the scapula. It exhibits : 1. The 

 glenoid cavity — an oval diarthrodial surface, excavated to a slight extent to receive 

 the head of the humerus, nbtched on the inner side, and bearing on the external 

 margin of the ridge which surrounds it a small tubercle of insertion. 2. The 

 coracoid process, situated in front, and at a certain distance from the glenoid 

 cavity. This is a large eminence in which may be distinguished two parts : the 

 base, a thick rugged process ; and the summit, a kind of beak curved inwards. 



Structure and development. — Like all the flat bones, the scapula is formed of 

 two compact layers separated by spongy tissue. The latter is very scanty 

 towards the middle of the supra- and infra-spinous fossfe, where it is often alto- 

 gether wanting ; it is most abundant in the angles. In Solipeds and Ruminants, 

 the scapula is developed from two principal centres of ossification, one of which 

 forms the coracoid process. 



In the Carnivora, the cartilage of prolongation is replaced by an epiphysary 

 lip. It may be added that in Mammaha, Meckel, Cuvier, and Strauss-Durckheim 

 have noted a supplementary nucleus in the glenoid cavity ; and that Lavocat 

 and Goubaux have observed it in Horses especially. Lavocat has described it as 



